44
votes
Accepted
Does the Earth constantly lose mass?
You are wrong that "to keep any object in circular motion requires energy"
In a circular orbit, the force of gravity is always perpendicular to the motion of the moon, so no work is done by ...
- 107k
28
votes
Accepted
How would "dark matter", subject only to gravity, behave?
What you describe is the standard paradigm in cosmological physics, so it has been studied extensively. The basic consequence of dark matter not having significant nongravitational interactions is ...
- 2,521
23
votes
Why does electron degeneracy pressure not stop massive star collapse?
You have the wrong idea about degeneracy pressure. There is no limit in principle on how closely together you can squeeze electrons (or other fermions) and at no point is the Pauli Exclusion Principle ...
- 136k
21
votes
Accepted
What is the mathematical condition for the statement: "gravitationally bound"?
It means the total energy (kinetic + gravitational potential) is negative. This assumes the convention that gravitational potential energy approaches zero as the distance tends to infinity, and is ...
- 107k
14
votes
Why does electron degeneracy pressure not stop massive star collapse?
A neutron star contains relatively few electrons.
In a white dwarf, electron degeneracy pressure does prevent further collapse. But if you add more matter to a white dwarf, it will shrink in volume, ...
- 107k
14
votes
Accepted
What is Gravitational softening length?
Gravitational softening is a numerical trick introduced in particle simulations to avoid too close encounters that would otherwise result in unrealistic motion of particles.
The gravitational force ...
- 35.9k
13
votes
Accepted
Could we detect dark matter by black holes gaining unexplained mass?
The accretion rate is far too small to make much difference to Galactic black holes, but how could this be distinguished from the accretion of normal, baryonic matter in any case?
In fact it is easier ...
- 136k
8
votes
Accepted
Is the speed of time much slower on sun surface?
Escape velocity from the surface of the Sun is 617.6 km/sec, or about 0.00206 times the speed of light. Denoting this ratio (escape velocity / speed of light) as $\beta$, time dilation at the surface ...
- 32.8k
7
votes
Could a rogue comet perturb a frequently occurring meteor shower to the extent that debris falls on Earth...and dislodges satellites?
Could it perturb?
No and yes. Meteor showers are made of meteroids in orbit around the sun, and the gravity of everything affects them, by the law of universal gravitation. But the meteors orbit in ...
- 107k
7
votes
Does the Earth constantly lose mass?
Earth does not lose mass to the moon's orbit. However, there are a few ways it can lose energy to gravitational effects. One way it can lose energy is to gravitational slingshotting, from satellites, ...
- 71
5
votes
Is it "nonsense to even talk about" objects outside the observable universe not having gravitational influence on us? (finite speed of gravity)
The earlier answer said
every point in the Universe has its own [observable universe], which implies that the objects near the edge of our [observable universe] could be effected by objects beyond ...
- 3,062
5
votes
Accepted
Farthest distance two objects are "gravitationally bounded", considering expansion of the Universe
Gravitational boundness is a tricky question. It's essentially asking, "will these two objects come together at any point in the future?" However, we can give approximate answers.
If there ...
- 2,521
5
votes
Eccentricity with a law of gravity different from the classical one
A planet following this law would either:
Follow a circular orbit. In this case the value of R would be constant and so the magnitude of the central force would also be constant, only the direction ...
- 107k
4
votes
How light could the lightest objects able to exist in a stable orbit be?
Here's one perspective. Newtonian gravity is symmetrical under two kinds of rescaling:
If you scale lengths and velocities by $\lambda$ and masses by $\lambda^3$, the system will evolve in exactly ...
- 2,521
4
votes
Accepted
Does a planets mass affect its gravitational pull? Let's say earth increased or decreased in mass could that theoretically affect gravity?
No, gravity is special, because it's pull is related to mass, but acceleration for a given force is inversely proportional to mass.
Galileo noticed this: he observed that two masses, one small and ...
- 107k
4
votes
Why does electron degeneracy pressure not stop massive star collapse?
You don't need quantum instrumentarium for a basic understanding of the compact star matters:
The inverse beta decay does not "violate" the exclusion principle. It simply removes electrons ...
- 2,756
4
votes
Why does electron degeneracy pressure not stop massive star collapse?
When an old star begins to collapse under its own gravity, one can in principle numerically solve the Schrödinger equation for the potential its electrons collectively experience. Although this is a ...
- 325
4
votes
What's the smallest scale at which dark matter has been measured?
Searches for dark matter particles in particle detectors have been unsuccessful thus far, so we must rely on astronomical observations.
What is the smallest scale at which we have detected "dark ...
- 4,354
4
votes
Accepted
Is the dark matter/baryonic matter ratio the same in galaxies with supermassive black holes?
Supermassive black holes (SMBHs) are primarily made of baryonic matter, not dark matter (DM).
Accretion disks
In order for the black hole to grow, it needs to accrete matter. In general, the ...
- 35.9k
4
votes
Gravitational-Wave Strain and Power (watt/square metre)
Some inital considerations. The total energy would depend on the length of time that the wave was continuous for, and the total area through which the wave passes. That is there is no hope to find ...
- 107k
3
votes
Physical Meaning of the Principal Tidal Fourier Modes and Their Integers
In that paper, we actually applied the term "principal" to the semidiurnal mode $\omega_{2200}$. When the planet is not synchronised (i.e., when it is not showing the same side to the ...
- 714
3
votes
Why does electron degeneracy pressure not stop massive star collapse?
In a Fermi gas of electrons, the electron energy reflects the pressure. If the highest energy electrons are relativistic, the equation of state softens: a density increase doesn't produce as much ...
- 1,277
3
votes
Could the universe expand forever even if there is no force (e.g., dark energy or eternal inflation) pushing it apart?
Without dark energy, the expansion of the universe will slow down (because of gravity). But it need not stop expanding and contract again. That's because it's possible the force of gravity is not ...
- 3,799
3
votes
Accepted
Does gravity extend out infinitely?
Does gravity extend out infinitely?
Does this technically mean that the gravity from celestial bodies extend out infinitely, even if it has a really tiny effect further out?
Basically yes, you've ...
- 30.8k
3
votes
Gravitational-Wave Strain and Power (watt/square metre)
As explained in the thread How does the gravitational wave strain from a rotating binary depend on the chirp mass, frequency and distance & what a short derivation looks like?
If $m_1$ and $m_2$ ...
- 1,512
2
votes
Could a rogue comet perturb a frequently occurring meteor shower to the extent that debris falls on Earth...and dislodges satellites?
en.wikipedia.org/wiki/Logarithm
Mass of a satellite: _000 kg, exceeding 10,000 kg for the biggest comsats.
Mass of a meteor particle: milligrams to possibly nanograms (0.00000_ kg to 0.00000000_ kg). ...
- 718
2
votes
What kind of effects would two moons have on an earthlike planet?
The combined gravitational force of two moons of mass X would be greater than the effect of one moon of mass X. That is obvious. Of course the two moons would orbit the planet with different periods ...
- 6,692
2
votes
Can objects join the Hubble flow for a given amount of time and then somehow abandon it?
Sufficiently large overdensities detach from the Hubble flow and collapse to form the structures we see in the Universe, i.e. galaxies, groups, clusters, and superclusters. The formation is "...
- 35.9k
2
votes
Accepted
At what point above Jupiter is the gravity Earth-like?
According to Newton, the gravitational acceleration of a spherical body is given by
$$a = \frac{GM}{r^2}$$
where $GM$ is the standard gravitational parameter and $r$ is the radial distance from the ...
- 11.8k
2
votes
Does the Earth constantly lose mass?
No energy is needed for the moon to keep going straight ahead in space that is curved by earth's gravity. Which makes "straight ahead" being orbital around the earth.
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Only top scored, non community-wiki answers of a minimum length are eligible